Macromonomers may be used to form comb or star shaped copolymers that are incorporated into compositions to enhance the properties of the composition. For example, the copolymer may include a polymeric backbone with a portion of the macromonomers forming side chains off of the backbone. The polymeric backbone may be derived from polar monomers, such as (meth)acrylates, while the macromonomers may be derived from non-polar monomers, such as butadiene or isoprene, that are polymerized and terminally functionalized. Examples of applications for such copolymers include viscosity index improvers for lubricant and hydraulic fluid compositions, water resistance additives for cosmetic compositions, and adhesion promoters in pressure sensitive adhesive compositions.
The macromonomers may be made by first manufacturing a precursor by anionic polymerization of a monomer, such as butadiene. Anionic polymerization allows for the control of the molecular weight, molecular weight distribution, and controlled reaction of the living chain ends. By controlling the macrostructure, rheological properties of the macromonomers can also be controlled. For example, it is known by those of skill in the art that molecular weight of the polymer is proportional to viscosity. Therefore, when a high molecular weight macromonomer is desired, the result may be a macromonomer of high viscosity that is difficult to process.
In many applications, consumers prefer that the macromonomer be provided in the form of a hydrogenated amorphous liquid. This may be accomplished by controlling the microstructure of the macromonomer and via hydrogenation. For example with respect to polybutadiene-based macromonomers, polar modifiers added to the solution for anionic polymerization, such as Lewis bases, are most often employed to control the level of vinyl structures in the resulting macromonomer. It has been reported that a minimum vinyl enchainment of 40% by weight is necessary to maintain a liquid, non-crystalline form for polybutadiene after hydrogenation.
Thus, there is a need for improved macromonomers and methods for obtaining macromonomers provided in the form of amorphous liquids that have relatively low viscosity for easier processing.